The present invention relates to a rocker arm for a valve train of an internal combustion engine which is pivoted on a bearing arrangement on a support pin (also known as a trunnion), whereby the support pin is connected with a cylinder head through a support block. The rocker arm is formed from a U-shaped metal element with at least two side walls that extend parallel to one another in the region of the support pin, which have aligned holes which each accommodate one radial roller bearing. In any case, an outer bearing ring of the radial roller bearing is arranged in each of the bore holes. The side walls are connected through an upper or a lower wall, so that a push rod contacts one end section of the rocker arm and a valve shaft of a gas exchange valve contacts the opposite end section.
Rocker arm arrangements of this type for controlling a valve train of internal combustion engines have been previously known for a long time. Such an arrangement is, for example, described in DE-OS 20 38 381. A U-shaped rocker arm open upwardly has two side walls which are connected with each other through a lower wall. This operating lever is pivoted on a support pin which once again is connected through a support block with the cylinder head of the internal combustion engine. A cam-actuated push rod contacts one end region of the rocker arm, and a valve shaft of a gas exchange valve contacts the other opposite end region. If now the push rod moves upward, the rocker arm swivels about its pivot axis so that its other end region is moved downward, so that the gas exchange valve is brought into the open position. The mounting of the rocker arm on the support pin takes place such that the rocker arm is held on both sides of the support block in needle bearings, the bearing outer ring of each of which is pressed into a through hole in the side wall in question.
Here it is disadvantageous that oblique angles of the push rod, caused by construction conditions, create axial forces. These axial forces lead to a sliding contact between rocker arm and its support arrangement or between the rolling elements and the end flanges within the radial roller bearing. This sliding contact unnecessarily increases friction, and therewith generates heat.
It is therefore the object of the invention to configure a bearing arrangement of a rocker arm for a valve train of an internal combustion engine such that the latter can accommodate axial forces without difficulty, in addition to the radial forces that arise.
This object is accomplished in accordance with the invention by providing a rocker arm which is pivotably connected by a bearing arrangement on a support pin, whereby the support pin is connected with a cylinder head through a support block. The rocker arm is formed as a U-shaped metal element with at least two side walls that extend parallel to one another in the region of the support pin which have aligned holes for each accommodating a radial roller bearing. An outer bearing ring of each of the radial roller bearings is arranged in the holes. The side walls are connected with each other through at least one of an upper and a lower wall so that a valve shaft of a gas exchange valve contacts one end section. An axial roller bearing is arranged at least in connection with one of the radial roller bearings.
This additional axial roller bearing replaces sliding friction arising in connection with an inclined position of the push rod with rolling friction and thus diminishes the overall amount of friction. This diminution of the overall amount of friction once again contributes to extending the life of the rocker arm arrangement.
Further advantageous developments of the rocker arm arrangement of the invention are described below.
In one aspect of the invention, the axial roller bearing is arranged internally or externally in connection with the radial roller bearing. The arrangement of the additional axial roller bearing is oriented according to the axial forces and overturning moments arising in any given case.
In another aspect, the radial roller bearing comprise two formed bearing rings manufactured by a chipless process which have at each opposite-lying end a radially inwardly directed rim and a radially outwardly directed rim. The axial roller bearing should include two thrust washers between which rolling elements located in a cage roll pass, whereby one thrust washer is braced on the radially inwardly directed rim and the other thrust washer is braced on a shoulder of the support pin. The radial inwardly directed rim of the outer ring and the shoulder of the support pin may also serve as the thrust surfaces for the axial rollers if properly prepared.
A particularly advantageous configuration of the rocker arm mounting results from the radial and the axial roller bearing being constructed as a one-piece assembly in the form of a combined radial-axial roller bearing. This compact assembly diminished the overall expenditure in assembling the rocker arm arrangement.
An especially advantageous embodiment of this combined radial-axial roller bearing provides the outer ring as well as the inner ring of the bearing being formed in a chipless process, which each have on their exterior sides a radially outwardly directed flange that acts as a thrust washer which serves as a raceway for the rolling element of the axial roller bearing.
Finally, a further additional feature provides that the outer bearing ring of the radial roller bearing has a radially inwardly directed rim, and the radially outwardly directed flange of the axial roller bearing has an axially oriented collar. In this way, it is assured that even in a cageless application, the rolling elements of the radial bearing as well as the rolling elements of the axial bearing cannot leave the combined bearing assembly.